The Measurement While Drilling (MWD) systems guide the drilling engineer to correctly project the direction of a new well according to the drilling plan. The MWD sensors (located about 15-20 m from the bit) include directional module (azimuth, inclination, rotation), vibration, background gamma radiation, and optionally: formation resistivity. Additionally, in order to obtain a more precise reading, the directional sensors are sometimes placed near the bit (Near Bit Sub).
The use of Resistivity tools in the MWD application currently has two main issues.
The mechanical connection between the Resistivity module and MWD tool is the weakest point of system. The need to install the MWD and Resistivity firmly in the drilling collar and the significant length of the combined string, calls for special ways to connect these instruments together. Two main solutions are now used: Telescopic Connector and Finger Rotary Connector.
Both of these connections have problems with: proper contact maintenance, lining up while assembly and flooding. Furthermore, any failure with the connector will also cause the failure of the entire combined system.
The length of the combined string is significant and it introduces additional mechanical stresses due to the flexing of the tools while drilling. causing premature failures from fatigue.